Audio coding systems like Dolby AC-3 and MPEG-2 Audio permit the transmission of high quality audio signals, especially the transmission of multi channel audio. Defining the possible configurations for reproduction by "x/y", wherein x is the number of the front channels and y is the number of the surround channels, then e.g. with Dolby AC-3 the following configurations for reproduction are possible: 3/2, 3/1, 2/2, 3/0, 2/1, 2/0, 1/0. In addition a low frequency channel can be transmitted.
In order to make possible such a multi channel sound reproduction the transmitted audio data stream has to be decoded by an appropiate multi channel audio decoder. In case, however, the device designated for reproduction contains only a two channel audio decoder then a multi channel audio reproduction can be performed only by using an external multi channel audio decoder. The audio data are output therein via a serial digital interface from the reproduction device to the multi channel decoder. In case the output of the audio signals shall occur in companying a video signal as for example for reproduction of a movie stored on a DVD, a method for synchronization is needed in order to achieve a lip synchronization between reproduction of picture and multi channel sound.